Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, and is suitable to an image pickup optical system used in an image pickup apparatus, e.g., a digital camera, a video camera, a TV camera, a monitoring camera, or a silver-halide film camera.
Description of the Related Art
As an image pickup optical system used in an image pickup apparatus, there is demanded an image pickup optical system, which is capable of moving a focus lens at high speed and with high accuracy during focusing, and which is reduced in image magnification change during focusing.
A lens unit arranged closest to an object side in the image pickup optical system tends to be increased in size and weight. Therefore, there is known a zoom lens, which uses, for focusing, a lens unit arranged on an image side of the lens unit arranged closest to the object side.
In Japanese Patent Application Laid-Open No. 2015-72499, there is disclosed a zoom lens, including in order from an object side to an image side a first lens unit to a fifth lens unit having positive, negative, positive, negative, and positive refractive powers, and in which the fourth lens unit is configured to move during focusing.
In Japanese Patent Application Laid-Open No. 2013-011914, there is disclosed a zoom lens, including in order from an object side to an image side, a first lens unit to a sixth lens unit having positive, negative, positive, negative, positive, and positive refractive powers, and in which the fourth lens unit is configured to move during focusing.
In Japanese Patent Application Laid-Open No. 2006-227526, there is disclosed a zoom lens, including in order from an object side to an image side a first lens unit to a fifth lens unit having positive, negative, positive, negative, and positive refractive powers, and in which the second lens unit is configured to move during focusing.
In Japanese Patent Application Laid-Open No. H11-44848, there is disclosed a zoom lens, including in order from an object side to an image side a first lens unit to a fifth lens unit having positive, negative, positive, negative, and positive refractive powers, and in which a part of the second lens unit is configured to move during focusing.
In Japanese Patent Application Laid-Open No. 2008-292562, there is disclosed a zoom lens, including in order from an object side to an image side, a first lens unit to a fourth lens unit having positive, negative, positive, and positive refractive powers, and in which the second lens unit is configured to move during focusing.
In general, when the number of constituent lenses of the focus lens unit is reduced in order to reduce the focus lens unit in size and weight, residual aberrations in the focus lens unit are increased. Therefore, the aberration variations during focusing are increased, and hence it becomes difficult to obtain good optical performance over the entire object distance from a long distance to a short distance.
Meanwhile, when a refractive power of the focus lens unit is reduced in order to reduce the aberration variations during focusing, a movement amount of the focus lens unit during focusing is increased, and a total length of the zoom lens is increased. In order to obtain a zoom lens having a small size as the entire system, being capable of performing focusing at high speed, and having small aberration variations and a small image magnification change during focusing, it is important to appropriately set the number of lens units, the refractive powers of the respective lens units, a lens configuration, and the like.